> I have no problem with adding this discussion to the single file work, but I'm not sure that would speed it up? Seems like this is a pretty independent addition to the metadata layout?
Yes, it is fairly independent. The main reason I wanted to consolidate in the doc, it appears there is a bit of metadata re-arrangement and new fields. I wanted to make sure that: 1. We avoid field ID conflicts. 2. When writing up the final spec changes it is easy to manage and not create a dependency one way or another between the two of these. Happy to keep the implementation of the guard-rails as a separate piece of work. Cheers, Micah On Fri, Dec 19, 2025 at 7:31 AM Russell Spitzer <[email protected]> wrote: > I have no problem with adding this discussion to the single file work, but > I'm not sure that would speed it up? Seems like this is a pretty > independent addition to the metadata layout? > > On Thu, Dec 18, 2025 at 6:28 PM Micah Kornfield <[email protected]> > wrote: > >> Thanks for the clarification, Micah! I want to explicitly call out (and >>> double-confirm) the key principle here: all tags must be strictly optional >>> and never required for correctness or basic functionality. Engines should >>> always be able to safely drop or ignore tags without breaking reads or >>> writes, with the only possible impact being suboptimal behavior (e.g., >>> extra I/O), as you described. >> >> >> 100% I will also add this summary to the bottom of the requirements >> section. >> >> Based on mailing list discussion and doc comments (or lack thereof), it >> does not seem like there are strong objections to adding this for V4. >> Prashant seemed to maybe have concerns, so I'd like to understand if they >> are blockers. >> >> If there isn't additional feedback by the end of next week, I'd like to >> assume a lazy consensus and consolidate this with the single file >> improvement work, which has already reorganized the metadata schema [1]. >> Please let me know if there is a different process. >> >> Thanks, >> Micah >> >> [1] >> https://docs.google.com/document/d/1k4x8utgh41Sn1tr98eynDKCWq035SV_f75rtNHcerVw/edit?tab=t.0#heading=h.unn922df0zzw >> >> On Wed, Dec 17, 2025 at 5:38 PM Yufei Gu <[email protected]> wrote: >> >>> Thanks for the clarification, Micah! I want to explicitly call out (and >>> double-confirm) the key principle here: all tags must be strictly optional >>> and never required for correctness or basic functionality. Engines should >>> always be able to safely drop or ignore tags without breaking reads or >>> writes, with the only possible impact being suboptimal behavior (e.g., >>> extra I/O), as you described. >>> >>> As long as this constraint is clearly stated and enforced, the trade-off >>> feels reasonable to me. >>> >>> Yufei >>> >>> >>> On Mon, Dec 15, 2025 at 4:28 PM Micah Kornfield <[email protected]> >>> wrote: >>> >>>> Hi Yufei, >>>> >>>>> If one engine started to rely on a tag for certain reasons(like >>>>> clustering algorithm), would data file rewrite(compaction) by another >>>>> engine remove the tag, and break the engine relying on it. >>>> >>>> >>>> The intent here is that dropping tags should never break an engine. >>>> But it could cause suboptimal operations. For instance, one example I >>>> brought in the docs is using tags to cache parquet footer size, to make >>>> sure it is fetched in 1 I/O. >>>> >>>> In this case the following would occur. >>>> >>>> 1. Engine 1 does a write to file 1 and records its footer size in tags. >>>> 2. Engine 2 does a rewrite/compactions and produces File 2 without >>>> tags. >>>> 3. Engine 1 then tries to read file 2. The tag for footer length is >>>> missing so it falls back reading a reasonable number of bytes from the end >>>> of the parquet file, hoping the entire footer is retrieved (and if it isn't >>>> a second I/O is necessary). >>>> >>>> Similarly for clustering algorithms, I think the result could yield a >>>> sub-optimally clustered table, or perhaps redundant clustering operations >>>> but shouldn't break anything. This is no worse then the case today though >>>> if engine 1 and engine 2 have different clustering algorithms and they are >>>> being run in interleaved fashion on the same table. In this case it is >>>> highly likely that some amount of duplicate compaction is happening. >>>> >>>> In the current proposal, any metadata that is required for proper >>>> functioning should never be put in tags. >>>> >>>> Thanks, >>>> Micah >>>> >>>> >>>> On Mon, Dec 15, 2025 at 4:02 PM Yufei Gu <[email protected]> wrote: >>>> >>>>> Thanks for the proposal! >>>>> >>>>> If one engine started to rely on a tag for certain reasons(like >>>>> clustering algorithm), would data file rewrite(compaction) by another >>>>> engine remove the tag, and break the engine relying on it. >>>>> >>>>> Yufei >>>>> >>>>> >>>>> On Wed, Dec 10, 2025 at 2:58 PM Micah Kornfield <[email protected]> >>>>> wrote: >>>>> >>>>>> Hi Iceberg Dev, >>>>>> I added a proposal [1] to add a key-value tags field for files in V4 >>>>>> metadata [2]. More details are in the document but the intent is to >>>>>> allow >>>>>> engines to store optional metadata associated with these files: >>>>>> >>>>>> 1. The proposed field is optional and cannot be used for metadata >>>>>> required for reading the table correctly. >>>>>> 2. It also proposes guard-rails for not letting tags cause metadata >>>>>> bloat. >>>>>> >>>>>> Looking forward to hearing everyone's thoughts and feedback. >>>>>> >>>>>> Thanks, >>>>>> Micah >>>>>> >>>>>> [1] https://github.com/apache/iceberg/issues/14815 >>>>>> [2] >>>>>> https://docs.google.com/document/d/16flxDXjpBiAs_cF3sjCsa7GlvSHQ0Mmm74c8yvYQlSA/edit?tab=t.0#heading=h.cnpb2lth3egz >>>>>> >>>>>>
